The applicants have developed a compact and inexpensive optical scanner which is based on a novel principle. This scanner is disclosed in Japanese Patent Publication 4-95917. FIG. 1 shows a simplified perspective view of such a scanner designated generally as optical scanner A. Scanner A comprises a vibrator 1, formed from a thin plate, and a small drive source 2. The drive source 2 comprises a device which generates microscopic vibrations in a piezoelectric or magnetostrictive vibrator or the like. Vibrator 1 is shaped as shown in FIG. 1 and comprises an elastically deformable shaft 3, which functions as a torsion bar capable of deforming in at least the bending mode of deformation, a vibrational input segment 4 disposed at one end of the shaft 3, and a driven segment 5 disposal at another end of the shaft 3. The shaft 3, input segment 4, and driven segment 5 are formed as a unit from a single silicon wafer. Further, driven segment 5 is symmetrical with respect to an axis P of deformable shaft 3. Also, a mirror surface 6 is formed on the driven segment 5 by processing the surface of driven segment 5.
When vibrational input segment 4 is induced by drive source 2 to vibrate at a frequency equal to the resonant frequency f.sub.B of the bending mode of deformable shaft 3, shaft 3 vibrates in that mode, driven segment 5 vibrates by bending in a direction .THETA..sub.B, and driven segment 5 rotates in the direction .THETA..sub.B. If at this time a light beam .alpha. strikes mirror surface 6 on driven segment 5, the reflected light beam .alpha. will be scanned over an angle which is twice as large as the angle of rotation of driven segment 5.
If optical scanner A undergoes a severe shock or vibration resulting, for example, from being dropped or from unintentional vibration induced by drive source 2, the plastic deformation of shaft 3 may be affected and various parts of optical scanner A, in particular shaft 3, may be damaged. As a result, the scanning characteristics of optical scanner A may change significantly in which case it is possible that the proper scanning angle of reflected light beam .alpha. will not be achieved, or even that light beam .alpha. will no longer be scanned.